UIViewController maintains state after being nilled - objective-c

Question

In my app, I made a BookViewController class that displays and animates the pages of a book and a MainMenuViewController class that displays a set of books the user can read.
In the latter class, when the user taps on one of the books, a function is called that should create a completely new instance of BookViewController, but for some reason the instance maintains its state (i.e. it resumes from the page the user left off).
How can this be if I set it to nil? What am I missing here? (Note that I'm using ARC).
MainMenuViewController.m
#interface MainMenuViewController ()
#property (strong) BookViewController *bookViewController;
#end
#implementation MainMenuViewController
#synthesize bookViewController;
-(void)bookTapped:(UIButton *)sender{
NSString *bookTitle;
if(sender == book1button) bookTitle = #"book1";
else if(sender == book2button) bookTitle = #"book2";
bookViewController = nil;
bookViewController = [[BookViewController alloc] initWithBookTitle:bookTitle];
[self presentViewController:bookViewController animated:YES completion:nil];
}
BookViewController.h
#interface BookViewController : UIViewController
-(id)initWithBookTitle:(NSString *)bookTitle;
#end
BookViewController.m
#implementation BookViewController
-(id)initWithBookTitle:(NSString *)theBookTitle{
self = [super init];
if(self){
bookTitle = [NSString stringWithFormat:#"%#", theBookTitle];
[self setModalTransitionStyle:UIModalTransitionStyleCrossDissolve];
NSLog(#"init a BookViewController with bookTitle: %#", bookTitle);
}
return self;
}
edit 1:
Every time a book is tapped, bookTapped: is called, and thee console always prints:
2012-08-31 16:29:51.750 AppName[25713:c07] init a BookViewController with bookTitle: book1
So if a new instance of BookViewController is being created, how come it seems to be returning the old one?
edit 2:
I inserted NSLog(#"bookViewController %#",bookViewController); just before the line [self presentViewController:bookViewController. The console output is:
2012-08-31 16:37:41.426 Henry[25784:c07] bookViewController <BookViewController: 0x6a21540>
2012-08-31 16:38:23.321 Henry[25784:c07] bookViewController <BookViewController: 0xe425540>
2012-08-31 16:38:53.393 Henry[25784:c07] bookViewController <BookViewController: 0x6839330>

Answer 1

Your variables are declared outside of the #implementation of the class (you are declaring global variables).

Answer 2

I suspect that you are using the ivars instead of the properties. Please replace bookViewController with self.bookViewController.
Try:
if(self){
self.bookTitle

Answer 3

The variables that were maintaing their state in the new instance were declared thus:
#import "BookViewController.h"
int currentPage = 0;
#implementation BookViewController
-(id)initWithBookTitle:(NSString *)theBookTitle{
...
So I managed to fix the issue by initialising the variables in the init method:
-(id)initWithBookTitle:(NSString *)theBookTitle{
self = [super init];
if(self){
currentPage = 0; //added this line
bookTitle = [NSString stringWithFormat:#"%#", theBookTitle];
[self setModalTransitionStyle:UIModalTransitionStyleCrossDissolve];
NSLog(#"init a BookViewController with bookTitle: %#", bookTitle);
}
return self;
}
But this doesn't solve the underlying problem, which is that doing this:
bookViewController = [[BookViewController alloc] initWithBookTitle:bookTitle];
[self presentViewController:bookViewController animated:YES completion:nil];
still presents a bookViewController with the old value for currentPage! This might be because I'm not declaring it as a property, nor initialising it in the init method... Any thoughts?